1. Field of the Invention
The present invention relates to image forming apparatuses, such as a copy machine, a printer, and a facsimile machine, which form an image by electrophotography or the like. In particular, the present invention relates to a developing apparatus which forms a toner image on an image bearing member using toner.
2. Description of the Related Art
In general, image forming apparatuses, such as a copy machine and a laser beam printer, which use electrophotography, form an image as follows. That is, a charging device uniformly charges a surface of an image bearing member (photosensitive drum), and the thus-charged surface is subjected to an exposure process based on an image using a semiconductor laser. As a result, an electrostatic latent image is formed. Then, a developing apparatus forms a toner image from the electrostatic latent image, and the toner image is transferred onto a transferring medium (recording medium). The toner image that is transferred onto the transferring member is fixed with heat and pressure by a fixing apparatus.
To increase the processing speed of the image forming apparatus and to improve the image quality, a developing apparatus structured as shown in FIG. 11 has been proposed (see Japanese Patent Laid-Open No. 3-168665). As shown in FIG. 11, according to Japanese Patent Laid-Open No. 3-168665, the processing speed can be increased because a photosensitive drum 301 is provided with a developing device 304 having developing sleeves 341 and 342.
Japanese Patent Laid-Open No. 2003-15412 describes another example of a developing apparatus including a plurality of developing sleeves. This developing apparatus includes a first developing sleeve and a second developing sleeve capable of swinging about the first developing sleeve. Each of the sleeves has a portion that is brought into contact with a photosensitive drum so that gaps (SD gaps) between the photosensitive drum and the sleeves can be stabilized and a gap between the two sleeves can be maintained constant. As a result, the image quality can be improved.
A magnetic body (magnetic roller) having magnetic poles is disposed in each of the developing sleeves, and it is necessary to place the magnetic poles at predetermined positions. In the case where, for example, the number of developing sleeves is one, the adjustment of the magnetic poles is generally performed as follows. That is, an end portion of the magnetic body is formed in a D-shape, and a fitting member that can be fitted to the D-shaped end portion is provided. The fitting member is rotated so that the magnetic poles can be placed at the desired positions. After the adjustment, the fitting member is fixed to a developer container. Thus, the positions of the magnetic poles can be adjusted.
However, in the case where one of a pair of developing sleeves swings about the other developing sleeve, if the positions of magnetic poles in the swingable developing sleeve are adjusted in a similar manner, the swingable developing sleeve would be fixed to the developer container and becomes incapable of swinging.